The present disclosure relates to valves. More particularly, it relates to high-speed valves useful, for example, with switch-mode hydraulic circuits.
Switch-mode hydraulics, analogous to switch-mode converters from the field of power electronics, is an emerging method of controlling hydraulic circuits. This concept utilizes a high-speed valve to switch between efficient on and off states, while temporarily storing energy in inductive and capacitive elements. The mean flow or pressure is controlled by the duty cycle, defined as the time in the on position divided by the switching period. Switch-mode hydraulics have been proposed for many end use applications, such as buck/boost converters, pumps, linear actuators, engine valve, and multiple actuators. The benefits of this approach are low cost, low weight, good response time, and improved efficiency over throttling valve control.
The valve in a switch-mode hydraulic circuit has a demanding set of competing requirements for the circuit to achieve good performance and high efficiency. A high performance circuit, defined by a fast response time and a low flow ripple, requires a fast valve switching frequency. However, a fast switching frequency creates three main challenges. First, high frequency valves typically use a low mass switching element to minimize the inertial actuation forces. The low mass typically correlates to a small flow area, requiring a balance between fully-open throttling loss and inertial force. Second, each switching event results in throttling across the partially-open transitioning valve. This energy loss can be minimized through soft switching or by reducing the valve transition time, at the expense of increasing the velocity of the switching element. Finally, each switching cycle incurs losses due to compressing and decompressing the fluid in the switched volume. The compressible energy loss can be minimized by reducing the switched volume between the valve and the inductive element.
Various known valve designs have been considered for switch-mode hydraulic circuit applications. For example, while the switching frequency limit for off-the-shelf solenoid valves is around 10 Hz, multiple researchers are attempting to develop high-speed valves specifically for switch-mode circuits. High-speed valve designs reported in the literature include: solenoid valves, poppet valves, linear spool valves, and continuously rotating axial and radial flow valves. Unfortunately, a viable valve design capable of optimally satisfying the high switching frequency and short valve transition requirements of switch-mode hydraulic circuits is not yet available.
In light of the above, a need exists for an improved valve architecture capable of providing a high switching frequency and useful, for example, with switch-mode hydraulic circuits.